The bodies of all but the simplest animals and plants are too large and too complex to survive the bursting and disruptive action of extreme cold, due to the unequal distribution of water within them and its irresistible expansion when frozen. Their living mechanism is broken, mechanically destroyed by this expansion. We cannot hope to apply cold to man so as to produce "suspended animation." It is true that experiments are on record in which fish and even frogs have survived enclosure within a solid mass of ice by the freezing of the water in which they were living. But careful experiments are wanting which would demonstrate that these animals were actually frozen through and through, and that either fish or other cold-blooded animals can survive a thorough solidification by freezing of their entire substance. Such survival cannot be pronounced to be impossible, but it has not been demonstrated in any cold-blooded animal–even shell-fish or worm or polyp–let alone a warm-blooded mammal. It appears that, apart from disruptive effects, the protoplasm of even very minute and simple organisms, such as the Protozoa, does not in all kinds, even if in any, survive exposure to great cold. The toleration of great cold and return to living activity after thorough freezing is, it appears, a special quality attained by the living material of vegetable seeds and by many kinds of bacteria. A similar special toleration of high temperatures, a good deal short of the boiling point, but high enough to kill most plants and animals, is known to characterize certain bacteria and allied Schizophyta found in hot springs. It is a matter of common knowledge that many animals and plants are killed by a temperature (whether too high or too low for them) which allows others to flourish and may be necessary for their life. Minute organisms (flagellate monads) have been cultivated experimentally in a nourishing liquid, the temperature of which was raised daily by one or two degrees until the liquid was so hot that the same species of organism was at once killed by it when abruptly transferred to it from liquid at ordinary summer temperature.